With this arrangement of the contact pins at the outer edge of the sleeve the problem exists of fixing the contact pins as securely as possible in order that they do not change their position during subsequent encapsulation of the sleeve and the inserted piezoelectric element with silicone or a similar material. Precise adherence to a predefined position is however absolutely essential in order that the upper contact surfaces of the contact pins are easily accessible for the connection of an electrical control unit after the installation of the actuator unit into the fuel injector. It is also necessary to ensure that the connecting parts still have a sufficiently large insulating gap with respect to adjacent metal parts because a relatively high control voltage is applied to the actuator. A further difficulty also consists in the fact that the mounting of the contact pins, to which the contact wires for the piezoelectric element are already soldered, is somewhat laborious because the contact pins are held only very loosely in the holes provided and can therefore easily slip when the parts are joined together.
Up until now these problems have only been inadequately solved. For example, for manufacturing related reasons a two-part plastic sleeve which has been turned over the piezoelectric element at the top and bottom has been used. When the two sleeve parts are joined together the sleeve is mechanically relatively unstable, and in particular the two contact pins can only be positioned very imprecisely. In addition, the engineering effort required for assembly is increased. Also, the two contact pins are inserted at the outer edge of the plastic sleeve into holes which are located on the upper end face of the plastic sleeve. With regard to this type of mounting, the contact pins are arranged to be relatively moveable, with the result that their position can easily change during encapsulation. This can then result in positioning errors affecting the contact pins in the finished encapsulated actuator unit, errors which can no longer be corrected. In the worst case the actuator unit can then not be used and must be singled out.